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Discusses test (also called MRI scan) that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body. Covers why it is done, how to prepare, and how it is done.

Magnetic Resonance Imaging (MRI)

Test Overview

Magnetic resonance imaging (MRI) is a
test that uses a magnetic field and pulses of radio wave energy to make
pictures of organs and structures inside the body. In many cases, MRI gives
different information about structures in the body than can be seen with an
X-ray,
ultrasound, or
computed tomography (CT) scan. MRI also may show
problems that cannot be seen with other imaging methods.

For an
MRI test, the area of the body being studied is placed inside a special machine
that contains a strong magnet. Pictures from an MRI scan are digital images
that can be saved and stored on a computer for more study. The images also can
be reviewed remotely, such as in a clinic or an operating room. In some cases,
contrast material may be used during the MRI scan to
show certain structures more clearly.

You may be able to have an MRI with an open machine that doesn't enclose your entire body. But open MRI machines aren't available everywhere. The pictures from an open MRI may not be as good as those from a standard MRI machine.

Why It Is Done

Magnetic resonance imaging (MRI) is
done for many reasons. It is used to find problems such as tumors, bleeding,
injury, blood vessel diseases, or infection. MRI also may be done to provide
more information about a problem seen on an X-ray, ultrasound scan, or CT scan.
Contrast material may be used during MRI to show abnormal tissue more clearly.
An MRI scan can be done for the:

Head. MRI can look at the brain for tumors, an
aneurysm, bleeding in the brain, nerve injury, and
other problems, such as damage caused by a
stroke. MRI can also find problems of the eyes and
optic nerves, and the ears and
auditory nerves.

Chest. MRI of the chest can look at the heart, the
valves, and
coronary blood vessels. It can show if the heart or
lungs are damaged. MRI of the chest may also be used to look for
breast cancer.

Blood vessels. Using MRI to look at blood vessels
and the flow of blood through them is called
magnetic resonance angiography (MRA). It can find
problems of the arteries and veins, such as an aneurysm, a blocked blood
vessel, or the torn lining of a blood vessel (dissection). Sometimes contrast
material is used to see the blood vessels more clearly.

Abdomen and pelvis. MRI can find problems in the
organs and structures in the belly, such as the liver, gallbladder, pancreas,
kidneys, and bladder. It is used to find tumors, bleeding, infection, and
blockage. In women, it can look at the uterus and ovaries. In men, it looks at
the prostate.

Bones and joints. MRI can check for problems of the
bones and joints, such as
arthritis, problems with the
temporomandibular joint,
bone marrow problems, bone tumors,
cartilage problems, torn
ligaments or
tendons, or infection. MRI may also be used to tell if
a bone is broken when X-ray results are not clear. MRI is done more commonly
than other tests to check for some bone and joint problems.

How To Prepare

Before your MRI test, tell your doctor
and the MRI technologist if you:

Are allergic to any medicines. The contrast material used for MRI does not contain iodine. If you know that you are allergic to the contrast material used for the MRI, tell your doctor before having another test.

Have a health condition, such as diabetes, sickle cell anemia, or kidney problems. You may need to change your medicine schedule. And some conditions may prevent you from having an MRI using contrast material.

Are or might be pregnant.

Have any metal implanted in your body. This helps your doctor know if the test is safe for you. Tell your doctor if you have:

Heart and blood vessel devices such as a coronary artery stent, a pacemaker, an ICD (implantable cardioverter-defibrillator), or a metal heart valve.

Metal pins, clips, or metal parts in your body, including artificial limbs and dental work or braces.

Any other implanted medical device, such as a medicine infusion pump or a cochlear implant.

Cosmetic metal implants, such as in your ears, or tattooed eyeliner.

Had recent surgery on a blood vessel. In some cases, you may not be able to have the MRI test.

Have an intrauterine device (IUD) in place. An IUD may prevent you from having the MRI test done.

Become very nervous in confined spaces. You need to lie very still inside the MRI magnet, so you may need medicine to help you relax. Or you may be able to have the test done with open MRI equipment. It is not as confining as standard MRI machines.

Wear any medicine patches. The MRI may cause a burn at the patch site.

You may need to arrange for someone to
drive you home after the test, if you are given a medicine (sedative) to help you relax.

For an MRI
of the abdomen or pelvis, you may be asked to not eat or drink for several
hours before the test.

You may need to sign a consent form that says you understand the risks of the test and agree to have it done.

Talk to your
doctor about any concerns you have regarding the need for the test, its risks,
how it will be done, or what the results will mean. To help you understand the
importance of this test, fill out the
medical test information form(What is a PDF document?).

How It Is Done

A magnetic resonance imaging (MRI)
test is usually done by an MRI technologist. The pictures are usually
interpreted by a
radiologist. But some other types of doctors can also
interpret an MRI scan.

You will need to remove all metal objects
(such as hearing aids, dentures, jewelry, watches, and hairpins) from your body
because these objects may be attracted to the powerful magnet used for the
test.

You will need to take off all or most of your clothes,
depending on which area is examined (you may be allowed to keep on your
underwear if it is not in the way). You will be given a gown to use during the
test. If you are allowed to keep some of your clothes on, you should empty your
pockets of any coins and cards (such as credit cards or ATM cards) with scanner
strips on them because the MRI magnet may erase the information on the
cards.

During the test, you usually lie on your back on a table that
is part of the MRI scanner. Your head, chest, and arms may be held with straps
to help you remain still. The table will slide into the space that contains the
magnet. A device called a coil may be placed over or wrapped around the area to
be scanned. A special belt strap may be used to sense your breathing or
heartbeat. This triggers the machine to take the scan at the right time.

Some people feel nervous (claustrophobic) inside the MRI magnet. If this
keeps you from lying still, you can be given a medicine (sedative) to help you
relax. Some MRI machines (called open MRI) are now made so that the magnet does
not enclose your entire body. Open MRI machines may be helpful if you are
claustrophobic, but they are not available everywhere. The pictures from an
open MRI may not be as good as those from a standard MRI machine.

Inside the scanner you will hear a fan and feel
air moving. You may also hear tapping or snapping noises as the MRI scans are
taken. You may be given earplugs or headphones with music to reduce the noise.
It is very important to hold completely still while the scan is being done. You
may be asked to hold your breath for short periods of time.

During
the test, you may be alone in the scanner room. But the technologist will watch
you through a window. You will be able to talk with the technologist through a
two-way intercom.

If contrast material is needed, the technologist
will put it in an
intravenous (IV) line in your arm. The material may be
given over 1 to 2 minutes. Then more MRI scans are done.

An MRI
test usually takes 30 to 60 minutes but can take as long as 2 hours.

How It Feels

You will not have pain from the magnetic
field or radio waves used for the MRI test. The table you lie on may feel hard,
and the room may be cool. You may be tired or sore from lying in one position
for a long time.

If a contrast material is used, you may feel some
coolness and flushing as it is put into your IV.

In rare cases,
you may feel:

A tingling feeling in the mouth if you have
metal dental fillings.

Warmth in the area being examined. This is
normal. Tell the technologist if you have nausea, vomiting, headache,
dizziness, pain, burning, or breathing problems.

Risks

There are no known harmful effects from the
strong magnetic field used for MRI. But the magnet is very powerful. The magnet
may affect pacemakers, artificial limbs, and other medical devices that contain
iron. The magnet will stop a watch that is close to the magnet. Any loose metal
object has the risk of causing damage or injury if it gets pulled toward the
strong magnet.

Metal parts in the eyes can damage the
retina. If you may have metal fragments in the eye, an
X-ray of the eyes may be done before the MRI. If metal is found, the MRI will
not be done.

Iron pigments in tattoos or tattooed eyeliner can
cause skin or eye irritation.

An MRI can cause a burn with some
medicine patches. Be sure to tell your health professional if you are wearing
a patch.

There is a slight risk of an
allergic reaction if contrast material is used during
the MRI. But most reactions are mild and can be treated using medicine. There
also is a slight risk of an infection at the IV site.

Results

A
magnetic resonance imaging (MRI) is a test that uses a
magnetic field and pulses of radio wave energy to make pictures of organs and
structures inside the body.

The
radiologist may discuss initial results of the MRI
with you right after the test. Complete results are usually ready for your
doctor in 1 to 2 days.

An MRI can sometimes find a problem in a
tissue or organ even when the size and shape of the tissue or organ looks
normal.

Magnetic resonance imaging (MRI)

Normal:

The organs, blood vessels, bones, and
joints are normal in size, shape, appearance, and location.

No abnormal growths, such as tumors, are
present.

No bleeding, abnormal fluid, blockage in
the flow of blood, or bulges in the blood vessels (aneurysms) are
present.

No signs of inflammation or infection are
present.

Abnormal:

An organ is too large, too small, damaged,
or absent.

Abnormal growths (such as tumors) are
present.

Abnormal fluid from a cause such as
bleeding or an infection is present. Fluid is found around the lungs or heart.
Fluid is found around the liver, bowel, or other organ in the
abdomen.

A blood vessel is narrowed or blocked. An
aneurysm is present.

Blockage in the gallbladder
bile ducts or in the tubes (ureters) that
lead out of the kidneys is present.

What Affects the Test

Reasons you may not be able to
have the test or why the results may not be helpful include:

Pregnancy. An MRI test usually is not done
during pregnancy. But MRI may be done to get more information about a possible
problem that cannot be seen clearly with
ultrasound.

Medical devices that use
electronics, such as a pacemaker or medicine infusion pump. The MRI magnet may
cause problems with these devices, and that may keep you from having an
MRI.

Medical devices that have metal in them. The metal might make
some of the detailed MRI pictures blurry. This may prevent your doctor from
seeing the organ that is being looked at. For example, an
intrauterine device (IUD) with metal may prevent your
doctor from seeing the uterus clearly.

Inability to remain still
during the test.

Obesity. A person who is very
overweight may not fit into standard MRI machines.

Many modern medical devices that do not use
electronics—such as heart valves, stents, or clips—can be safely placed in most
MRI machines. But some newer MRI machines have stronger magnets. The safety of
MRI scans with these stronger MRI magnets in people with medical devices is not
known.

What To Think About

Sometimes your MRI test results may be
different from the results of CT, ultrasound, or X-ray tests, because the MRI
scan shows tissue differently.

MRI is a safe test for looking at
structures and organs inside the body. It costs more than other methods and may
not be available in your area.

Open MRI machines are now made so
that the magnet does not completely surround you. But these machines may not be
available in all medical centers. Open MRI is useful for people who are
claustrophobic or obese.

MRI
spectroscopy is a special MRI method that identifies certain medical problems
by looking for specific chemicals in body tissues.

Contrast material that contains gadolinium may cause a
serious skin problem (called nephrogenic fibrosing dermopathy) in people with
kidney failure. Before having an MRI scan, tell your
doctor if you have serious kidney disease or if you have had a kidney
transplant.

MRI can be used to check different parts
of the body, such as the head, belly, breast, spine, shoulder, and knee.

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